The present invention is concerned with a brake pressure regulator for a hydraulic brake system for use with automotive vehicles provided with an anti-locking device and/or a traction skid control.
Brake pressure regulators for preventing automotive wheels from locking during deceleration are being increasingly employed in automotive vehicles. Such brake systems, in a large number of cases, are equipped with a brake force booster. In employing brake force boosters, the booster either can play a passive part in the regulating mode or the brake force booster itself can be incorporated into the regulating mode. Stated differently: the brake force booster, in conventional anti-locking devices, either can perform its brake force boosting function only in the normal brake mode or it can actively participate in the pressure modulation.
In one type of brake pressure regulator including brake force boosters, the brake force boosters are actively incorporated into the brake pressure regulation. Such brake force boosters of the hydraulic type, which cooperate with a pressure modulator for pressure modulation in accordance with one or more control algorithms stored in an electronic regulator, are well known in the art.
For example, German Offenlegungsschrift No. 3612793 discloses a hydraulic brake system for automotive vehicles provided with an anti-locking control exhibiting the following characteristics. Being an anti-locking regulator, such a brake system includes a master brake cylinder operated with a first pressure fluid, and a brake force booster mechanically acting on the master brake cylinder and operated with a second pressure fluid, with the brake force booster being operable as a pressure modulator for the anti-locking control and check valves being respectively provided in the brake conduits leading from the master brake cylinder to the wheel cylinders.
In such brake systems, the brake force booster is a known hydraulic brake force booster including a pressure conduit connection capable of being connected to a hydraulic pressure source, and at least one return conduit connection capable of being connected to the reservoir which also includes an auxiliary connection in communication with the working chamber thereof. The pressure modulation during the anti-locking control, on the one hand, is generated by the working piston of the brake force booster and, on the other hand, is generated by a special modulation member independent thereof.
To explain the problem basic to the present invention, reference will be made in closer detail to the construction and operation of the subject matter of FIG. 2 of German Offenlegungsschrift No. 3612793.
In the normal brake mode, pressure fluid from the pressure source is supplied to the booster to move the working piston of the booster. The working piston, in turn, moves a push rod which, in turn, moves the working piston of the master cylinder.
The anti-locking control mode in the central control area, i.e., under uniform road conditions, operates as follows: the control solely relies on the auxiliary piston also called a modulation member. Once a pressure reduction during the control mode is required, hydraulic pressure is applied to the modulation member (from the left in FIG. 2). It is, therefore, moved to the right, returning the working piston of the booster to the right. The working chambers of the master cylinder are thereby pressure-relieved. Once pressure stability is required during the control mode, the pressure modulation member is hydraulically blocked, i.e., the pressure chambers to the left and to the right of the modulator member will be locked.
Once a pressure re-increase in the control mode is required, pressurized fluid will be discharged from the chamber to the left of the modulator member and the modulator member will move to the left. The booster piston also moves to the left. Also, the working piston of the master cylinder moves to the left, thereby attaining a pressure build-up in the wheel cylinders. In the central control area, the control is thus solely achieved by the modulator member and the electromagnetic valves, respectively, that are associated with the modulator member.
The pressure to the left of the modulator member is regulated by a passage valve and by a blocking valve. The pressure in the chamber to the right of the modulator member is regulated by a blocking valve and by a passage valve.
In the event of an abrupt change in the friction coefficient or in a skid, substantial pressure variations in the wheel cylinders will become necessary. In that situation, the working piston of the booster will become operative. The working piston will also become operative once the brake system operates in the traction skid control mode.
The anti-locking control mode, incorporating the working piston of the booster, is carried out as follows: the working piston (in FIG. 2 of said Offenlegungsschrift, on the left hand side thereof) is exposed to an application of pressure controlled by a blocking valve and a passage valve. The pressure to the right of the working piston of the booster is controlled by a blocking valve and a passage valve. As conveyed in the subject matter of Offenlegungsschrift No. 3612793, large volumes of fluid will have to be moved very frequently. for moving the volumes of fluid, only very short time intervals are available. The modulator piston according to the aforementioned Offenlegungsschrift requires a substantially larger effective cross-section or driving face than the transmission piston, thereby permanently circulating substantial volumes of fluid.
For the foregoing reasons, brake systems of the type of described in Offenlegungsschrift no. 3612793 and systems of a similar construction are less suitable for use in multiplex operation. In practice, it has been found, in addition, to be disadvantageous with state-of-the-art brake pressure regulators that, in view of the large volumes of fluid to be circulated, high dynamic pressures develop in the modulator compartment. Not only do such high pressures hamper the multiplex operation of the brake system, but they also effect any normal decelerating operation. In the state-of-the-art systems, large valve cross-sections are, therefore, required. The volume consumption of the state of art regulators is correspondingly high.
Thus, it would be desirable that the aforedescribed disadvantages involved with the state of art brake pressure regulators be avoided. It is intended to provide a brake pressure regulator which is suitable for multiplex operation. Moreover, it is an object of the invention to provide a brake pressure regulator having low mechanical design costs and which is capable of being employed for anti-locking control and traction skid control. Further, the construction of the brake pressure regulator is largely to be based on existing components. In the anti-locking control mode and in the traction skid control mode, comparatively low volumes of fluids are to be circulated. Finally, consumption of pressure fluid during the control mode is also to be reduced.